Crystalline silicon carbide exists in two basic forms, .alpha.-silicon carbide and .beta.-silicon carbide. In .beta.-silicon carbide, the crystals are cubic in nature. In .alpha.-silicon carbide, the crystals are rhombohedral or comprise stacked hexagonal layers. See Davis et al., Thin Film Deposition and Microelectronic and Optoelectronic Device Fabrication and Characterization in Monocrystalline Alpha and Beta Silicon Carbide, invited paper, Proceedings of the IEEE, Vol. 79, No. 5, May 1991.
There are over 100 different types (known as polytypes) of .alpha.-silicon carbide. The most common is 6H .alpha.-silicon carbide, which has a crystal structure in which six Si-C double sheets or layers are stacked atop one another to form a single lattice cell. Another form of .alpha.-silicon carbide which has been recently developed is 2H .alpha.-silicon carbide. In this material, the crystal structure is characterized in only two layers of Si-C double sheets being stacked atop of one another to form the lattice unit.
Silicon carbide exhibits a number of interesting properties. It has a large band-gap, high thermal conductivity, good radiation resistance, reasonable charge carrier mobilities, and excellent chemical and physical stability at temperatures in excess of 1,000.degree. C. For this reason, it has been proposed to use silicon carbide in a wide variety of different applications, including optical applications such as in the formation of optical coatings and the like. To date, however, use of silicon carbide for such utilities has been limited because of the inability to grow thin films from this material.
Recently, however, a number of techniques have been successfully used to produce silicon carbide in the form of thin films. Various deposition techniques, such as vapor phase epitaxy and molecular beam epitaxy, have been used for this purpose.
Unfortunately, none of these techniques has been able to produce 2H .alpha.-silicon carbide in thin film form. Molecular beam epitaxy produces .beta.-silicon carbide and amorphous silicon carbide, while vapor phase epitaxy and other chemical vapor deposition techniques produce polytypes other than 2H .alpha.-silicon carbide. Techniques currently known for producing 2H .alpha.-silicon carbide such as, for example, chemical vapor deposition using a mixture of hydrogen with methyltrichlorosilane (CH.sub.3 SiCl.sub.3) as reactants, uniformly produce small cylindrical crystals as product. See Ivanov et al., Recent development in SiC single-crystal electronics, Semiconductor Science Technology, Vol. 7, pp. 863-880, 1992; and Powell, Crystal Growth of 2H Silicon Carbide, Journal of Applied of Physics, Vol. 40, No. 11, pp. 4660-4662, October 1969.
Accordingly, it is an object of the present invention to provide a technique for forming thin films of 2H .alpha.-silicon carbide as well as the thin films so produced.